The subject invention relates to a pump for inflating rafts and similar inflatable devices, and in particular to such a pump which can provide either a large volume of air per stroke for initially filling the inflatable device, or a smaller volume of air per stroke for topping off a substantially filled inflatable device when its internal pressure has increased.
Many inflatable devices have to be filled or have air added to them at a remote location where only a hand-operated pump is available. Many inflatables, such as river rafts, contain a large volume of air. In order to fill them in a reasonable time with a hand pump the pump needs to deliver a relatively large volume of air with each stroke. However, as the raft approaches full inflation pressure, which is around 3 PSI, it becomes very difficult to operate a large volume hand pump. Thus, it is common to rely first on a high volume pump to initially fill the raft in the first instance, and then rely on a second lower volume pump which is easier to operate at higher pressures to top off the raft from time to time as required. This requires carrying two pumps in the raft. While two-stage pumps which serve both needs are available, they either are too large or cumbersome to carry on a-raft, or they have a pumping mechanism which is unreliable when exposed to water and sand, which a pump carried on a raft ultimately would be. Thus, the need remains for a single hand-operated pump, of a size that can be carried on a raft, having a simple dependable pumping mechanism which is not affected by sand and water that can provide both high volume of air to fill an empty or nearly empty raft and still be easy to operate as the raft becomes full and the pressure increases.